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GM Box Interchange - Provided by Jim 'Canuck' Campbell
A list of direct bolt-on boxes and some that need modifications.
(Note this list refers to Saginaw 605 Power boxes but would probably apply to manual as well.)

On some 64-70 the drag link hole on the pitman arm may need to be enlarged.

The following boxes will fit but may need to have the pitman arm and/or the rag joint changed or and extra bolt hole boss taked off the steering box. Make sure you compare the input shaft length or the length from the bolt holes to the end of the input shaft to your power box.

Use box from 1977-81 Camaro/Firebird with disc brakes (or any 800 series box used in Novas, full size GM, etc), gives approx 3 turns lock to lock, versus original power steering 4.5 turns.

All later model boxes require the 1964 - 72 Chevelle pitman PS arm (required change) when used on earlier Chevelles.

Steering shaft comes in two diameters, get the appropriate flex coupling lower half in the same style as original to match the boxes shaft.

1982 or 86 to 92 Comaro Z-28/firebird Trans-AM are 2 turns (12:1) lock to lock, Use original end cap to get the right stops on 2 turn boxes to decrease turning radius.

Later model boxes (1980 and up) use "O" rings instead of flared input and output lines.

Later model internals can be swapped into early boxes to eliminate problems with line fittings and stops or pump can be modified by changing outlet valve (this requires verification) or swapped to accept "O" ring hosed.

I hope you can maybe help me with my problem. I have a 1957 Chevy pickup that I am converting to 4X4 using parts from a 1979 Chevy 1/2 ton pickup. I have a Saginaw power steering box that has the pressure opening threads stripped. Is this an 11/16 opening with 18 threads? I need to get a tap and rethread the opening. I need to know what tap I need- can you or anybody out there help me out. Thanks Jim C

I don't have a hose handy that I can measure. Can you measure the hose end you have? Or use a "thread pitch gauge" that usually is in a tap & die set? A 11/16 should be an 18 where a 3/4 would be a 16.

You may not have enough room to use a tap unless you can find a "bottoming" tap that is not tapered much.

There was a switch from flared hose fittings to O-ring fittings sometime around your year. If it is a flare fitting, there should be a brass tapered seat at the bottom of the pressure hose hole. I have read that that can be pulled out, maybe by threading it and using a bolt. If you get it out, there would be more room for a tap.

I got the brass seat out and am trying to find an 11/16-18 tap to use. It looks like I might get this thing fixed! I appreciate the tips...I would not have enough room without removing that seat. thanks again
jim C

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